1. Field of the Invention
This invention relates to a precision polishing method and a precision polishing apparatus for polishing a semiconductor substrate. More particularly, the present invention relates to a precision polishing method and a precision polishing apparatus for flattening or removing the wiring material film formed on an insulating film of a semiconductor element in the process of manufacturing a semiconductor integrated circuit.
2. Related Background Art
The trend in recent years of producing semiconductor integrated circuits that are increasingly down-sized and multilayered is accompanied by the need for improved flattening technologies. A major advancement is brought forth in the filed of flattening technologies by chemical mechanical polishing (CMP).
FIG. 7 of the accompanying the drawing schematically illustrates a known chemical mechanical polishing (CMP) apparatus. As shown, it comprises a substrate-holding part 202 for removably holding a substrate 201 that may be a wafer with the surface to be polished facing downward and a polishing table 205 placed vis-a-vis the substrate 201 held by the substrate-holding part 202 and carrying a large caliber polishing pad 204 having a diameter greater than that of the substrate 201 as the latter is bonded thereto. The apparatus further comprises a first drive means 211 for driving the substrate-holding part 202 to revolve, a pressuring means 212 for applying pressure to the substrate 201 so as to make the surface, to be polished, of the substrate 201 pressed against polishing pad 204 and a second drive means 213 for driving the polishing table 205 to revolve, a polishing agent supply means 215 being additionally provided in order to supply the polishing pad 204 with a polishing agent 207.
With a polishing apparatus having a configuration as described above, the substrate 201 and the polishing pad 204 are driven to revolve respectively by the first drive means 211 and the second drive means 213 in the directions as indicated by the arrows in FIG. 7 so as to make the surface, to be polished, of the substrate 201 held by the substrate-holding part 202 abut the upper surface of the polishing pad 204 on the polishing table 205 and the pressurizing means 212 apply pressure to the substrate 201 to a predetermined pressure level to polish the surface while the polishing agent supply means 215 is operated to drop the polishing agent 207 onto the polishing pad 204. The polishing agent 207 is normally referred to as slurry that is a suspension prepared by mixing fine particles of silicon oxide, cerium oxide or alumina into an aqueous solution of potassium hydroxide or ammonium. Thus, the surface to be polished is flattened and smoothed by the combination of the chemical effect of the polishing agent and the physical effect of the polishing particles.
As described above, a polishing agent normally referred to as slurry that is a suspension prepared by mixing fine particles of silicon oxide, cerium oxide or alumina into an aqueous solution of potassium hydroxide or ammonium is used for CMP. Such a polishing agent is designed to be mainly used for polishing interlayer insulating films of semiconductor devices and hence can give rise to scratches on the metal surface when it is used for ductile metals such as copper (Cu) and aluminum (Al) and metal alloys containing them as principal ingredients as well as other problems including the problem of particles of the polishing agent buried into the metal surface. In the case of burying a tungsten (W) plug, where the plug has a small diameter between 0.5 and 1 xcexcm while the surface of the insulating film on the surface to be polished is far greater than the exposed surface of the tungsten plug and both tungsten and the material of the insulating film are fragile, the dishing problem can be alleviated to a certain extent by using a polishing pad showing an appropriate degree of compressibility.
However, in the process of forming wires from a metal film, particularly in a dual damascene process mainly using copper, the ratio of the exposed surface area of the insulating film to the surface area of the wiring metal is closer to 1 than the above instance so that conventional CMP techniques encounter the problem of a remarkable dishing phenomenon appearing on the wiring metal along with the problem of producing a process-altered layer near the surface of the object to be polished because the surface to be polished is subjected to pressure of a level between 200 to 500 gr/cm2 for the purpose of polishing.
In view of the unsolved problems of conventional techniques, it is therefore the object of the present invention to provide a precision polishing method and a precision polishing apparatus applicable to dual damascene processes involving the use of metal, highly ductile copper in particular, and adapted to be used with a chemical etching technique of utilizing a chemical effect for polishing a wiring metal film without producing any process-altered layer nor any scratches on the metal surface and without the risk of partly burying the polishing agent near the metal surface in order to flatten a smooth or remove the metal film.
In an aspect of the invention, the above object is achieved by providing a precision polishing method, comprising supplying an etching solution to the surface to be polished comprising the metal of a semiconductor device and flattening and removing said surface to be polished comprising said metal by utilizing a change of etching rate caused by the change of the temperature of the etching solution.
Preferably, with a precision polishing method according to the invention, a local temperature change is produced on the surface to be polished to cause said change of etching rate by locally applying heat to the semiconductor substrate having said surface to be polished or causing it to locally emit heat in order to produce a selective etching effect due to temperature difference, thereby flattening and removing said surface to be polished comprising said metal. Preferably, with a precision polishing method according to the invention, the temperature of the projecting areas of said metal in said surface to be polished is set higher than the temperature of the area other than said projecting areas of said metal in said surface to be polished and an abutting member is made to abut on said surface to be polished, thereby polishing and flattening said surface to be polished comprising the metal.
With a precision polishing method according to the invention, the projecting areas of the surface to be polished can be selectively caused to emit heat and raise the temperature thereof by making an abutting member abut on the surface to be polished with or without an etching solution interposed therebetween and driving the abutting member to move along and relative to the surface to be polished.
In another aspect of the present invention, there is provided a precision polishing apparatus adapted to polishing the surface to be polished comprising the metal of a semiconductor device by making the surface to be polished comprising the metal of a semiconductor device abut on a hard polishing pad under pressure of a predetermined level while supplying an etching solution to the surface to be polished and the abutment surface of said hard polishing pad and driving said surface to be polising to move relative to said polishing pad, thereby polishing said surface to be polished comprising the metal, said apparatus comprising at least either a means for locally raising the temperature of the projecting areas of said metal in said surface to be polished or a means for cooling the area other than said projecting areas of said metal in said surface to be polished so as to make the temperature of the projecting areas of said metal in said surface to be polished higher than the temperature of the area other than said projecting areas in said surface and utilize the change of etching rate caused by the change of the temperature of said etching solution supplied to said surface to be polished and the abutting surface of said hard polishing pad, thereby flattening and removing said surface to be polished comprising said metal.
Preferably, in a precision polishing apparatus according to the invention, a local temperature change is produced on and near the surface of a semiconductor substrate having said surface to be polished comprising the metal of the semiconductor device to cause said change of etching rate by locally applying heat to said semiconductor substrate or causing it to locally emit heat in order to produce a selective etching effect due to temperature difference, thereby flattening and removing said surface to be polished comprising said metal.
Preferably, in a precision polishing apparatus according to the invention, the projecting areas of the surface to be polished are selectively caused to emit heat and raise the temperature thereof by making the hard polishing pad abut on the surface to be polished with or without an etching solution interposed therebetween and driving the abutting member to move along and relative to the surface to be polished.
Preferably, in a precision polishing apparatus according to the invention further comprises a temperature control means for controlling the temperature of the etching solution. Preferably, a precision polishing apparatus according to the invention further comprises a collecting means for collecting said etching solution, a regulating means for filtering said etching solution and regulating its ingredients and a circulating means for circulating said etching solution.
Preferably, said metal of the semiconductor device is copper, aluminum, tungsten or an alloy containing at least one of the above listed metals. Preferably, said etching solution is a solution containing iron (III) chloride or copper (II) chloride, an alkaline aqueous solution containing a copper amine complex as principal ingredient or an etching solution containing a mixture of hydrogen peroxide and a sulfuric acid type solution. A polishing agent of fine solid particles with a primary particle size between 0.02 and 0.5 m may be added to the etching solution.
A precision polishing method and a precision polishing apparatus according to the invention may be applied to a dual damascene process, particularly to a dual damascene process mainly using copper.
According to the invention, there is also provided a precision polishing method adapted to polish the surface to be polished of a substrate by supplying liquid thereto, said method comprising the steps of supplying a chemical solution having an effect of etching projecting areas of metal on said surface to be polished as said liquid and controlling the temperature of said projecting areas of metal.
Preferably, a precision polishing method according to the invention further comprises a step of polishing said surface to be polishing by causing a hard polishing pad having a modulus of compressive elasticity between 9.8xc3x97107 Pa and 9.8xc3x971010 Pa, or 10 kgf/mm2 and 10,000 kfg/mm2 to abut on said surface to be polished. Preferably, with a precision polishing method according to the invention, said step of controlling the temperature of said projecting areas of metal is conducted by heating said projecting areas of metal by a heating means or by cooling the area of said surface to be polished other than said projecting areas of metal.
According to the invention, there is also provided a precision polishing method adapted to polish the surface to be polished of a substrate by supplying liquid thereto, said method comprising steps of supplying a chemical solution having an effect of etching projecting areas of metal on said surface to be polished as said liquid and polishing said surface to be polishing by causing a hard polishing pad having a modulus of compressive elasticity between 9.8xc3x97107 Pa and 9.8xc3x971010 Pa, or 10 kgf/mm2 and 10,000 kfg/mm2to abut said surface to be polished.
Preferably, a precision polishing method according to the invention further comprises a step of controlling the temperature of said projecting areas of metal.
According to the invention, there is also provided a precision polishing apparatus having a substrate-holding means for holding a substrate and a polishing pad holding member and adapted to polish the surface to be polished of said substrate by supplying liquid thereto, said apparatus comprising a supply means for supplying a chemical solution having an effect of etching projecting areas of metal on said surface to be polished as said liquid and a temperature control means for controlling the temperature of said projecting areas of metal.
Preferably, in a precision polishing apparatus according to the invention, said temperature control means is a cooling means for cooling the area of said surface to be polished other than said projecting areas of metal or a heating means for heating said projecting areas of metal. Preferably, in a precision polishing apparatus according to the invention, said polishing pad holding member removably holds a hard polishing pad having a modulus of compressive elasticity between 9.8xc3x97107 Pa and 9.8xc3x971010 Pa, or 10 kgf/mm2 and 10,000 kfg/mm2to abut said surface to be polished.
According to the invention, there is also provided a precision polishing apparatus having a substrate-holding means for holding a substrate and a polishing-pad-holding member and adapted to polish the surface to be polished of said substrate by supplying liquid thereto, said apparatus comprising a supply means for supplying a chemical solution having an effect of etching projecting areas of metal on said surface to be polished as said liquid, said polishing pad holding member removably holding a hard polishing pad having a modulus of compressive elasticity between 9.8xc3x97107 Pa and 9.8xc3x971010 Pa, or 10 kgf/mm2 and 10,000 kfg/mm2to abut said surface to be polished.
Preferably, a precision polishing apparatus according to the invention further comprises a temperature control means for controlling the temperature of said projecting areas of metal. Preferably, in a precision polishing apparatus according to the invention, said temperature control means is a cooling means for cooling the area of said surface to be polished other than said projecting areas of metal or a heating means for heating said projecting areas of metal.
Thus, with a precision polishing method and a precision polishing apparatus according to the invention, it is now possible to flatten and remove the metal film formed on a substrate by using an etching solution or a chemical solution adapted to principally exert a chemical effect in a polishing operation and show a selective etching rate that varies as a function of the temperature of the etching solution or the chemical solution.
Additionally, as a result of polishing the wiring metal film formed on an insulating film that is already flattened in a dual damascene process by utilizing the selective etching rate of an etching solution or a chemical solution that varies as a function of the temperature of the etching solution or the chemical solution, there is no risk of producing a dishing phenomenon on the metal surface. Still additionally, since no polishing agent that contains abrasive grains is used, there arises no risk of producing scratches on the metal surface nor that of partly burying the abrasive grains of the polishing agent near the metal surface. Furthermore, since the operating pressure applied to the substrate can be reduced unlike conventional CMP techniques, no process-altered layer would appear on and near the metal surface as a result of the polishing operation.
Finally, according to the invention, a substrate is polished by means of a precision polishing apparatus comprising one or more than on spiral type fluid flow paths as temperature control means arranged at least in the polishing head or the substrate-holding means. As fluid is made to flow through the flow paths, the entire surface to be polished of the substrate can be made to show a uniform temperature distribution. Then, the projecting areas of metal on the surface to be polished is heated as they are scraped by the polishing pad while the surface to be polished is held to show a uniform temperature distribution. As a result, the projecting areas show a high etching rate so that the metal film is accurately flattened.
Thus, with such a method and an apparatus, it is now possible to reliably form wires to be buried into wiring grooves or grooves for contact holes that are arranged in the insulating film on a semiconductor substrate.